Japanese Unexamined Patent Application Publication No. 2010-172069 (Patent Literature 1) discloses an in-wheel motor drive unit disposed in a road wheel internal space for a wheel, for example. The in-wheel motor drive unit of Patent Literature 1 includes a lubrication oil circuit of a center-shaft lubrication type. While the in-wheel motor drive unit is in operation, lubrication oil is discharged into the interior of the unit to lubricate a rotary shaft and gears inside the unit. As a result, the interior of the unit is sprayed with the lubrication oil, and an atmosphere of oil prevails inside the unit. Alternatively, an in-vehicle motor drive unit provided with another lubrication oil circuit of a bath lubrication type, instead of the center-shaft lubrication type, is known. The bath lubrication type employs rotation of a toothed wheel, such as an external gear, to splash lubrication oil and create an atmosphere of oil inside the unit. In any of both types, lubrication creates an atmosphere of oil inside the automotive motor drive unit, and the interior of the unit is sprayed with lubrication oil during operation.